Avermectin compounds are natural products produced by the fermentation of Streptomyces avermitilis as disclosed in U.S. Pat. No. 4,310,519 to Albers-Schonberg et al. The avermectin compounds have a natural .alpha.-L-oleandrosyl-.alpha.-L-oleandrosyloxy group at the 13-position. In U.S. Pat. No. 4,203,976 to Fischer et al certain synthetic procedures are disclosed for glycosylating various hydroxy groups or the avermectin molecule, including the 4"-hydroxy of the avermectin disaccharide group but not the 14a-position.